1. Field of the Invention
The present invention relates to a wavelength-division multiplex system that enables an efficient use of optical fibers and particularly to an improved method of setting wavelengths to be allocated to each transmission channel in such a wavelength-division multiplex system.
Recently, optical transmission systems provided with lines with larger capacity are being developed. Wavelength-division multiplexing (WDM) technology is becoming of an interest as a technology that is necessary for making efficient use of optical fibers.
FIG. 1 is a diagram showing an example of a WDM system. In the example shown in FIG. 1, the WDM system includes two WDM devices connected to each other. Each of the WDM devices includes a wavelength-converting unit (λ-converter) 110, a wavelength interface unit (I/F) 120 and a wavelength multiplexer/demultiplexer (MUX/DEMUX) 130. The wavelength-converting unit 110 receives signals of wavelength λs from downstream optical transmission devices 200-1 through 200-n and converts the wavelength λs into wavelengths λ1 through λn that are to be used on the upstream side of the wavelength-converting unit 110, or, used by the wavelength interface unit 120. In order to perform such a converting operation, the wavelength-converting unit 110 is configured using wavelengths λ1 through λn that correspond to channels of the wavelength interface unit 120. The wavelength interface unit 120 is provided with channels with predetermined wavelengths λ, i.e., λ1 through λn, that are fixed to and individually usable for the corresponding input terminals of the MUX/DEMUX 130 connected thereto. It is to be noted that in the following text, “upstream” is to be understood as a position along the transmission path nearer to the MUX/DEMUX 130 side and “downstream” is to be understood as a position along the transmission path nearer to the optical transmission devices 200-1, . . . , 200-n. 
Signals of wavelengths λ1 through λn that are output from upstream output terminals of the wavelength interface unit 120 are received and multiplexed by the MUX/DEMUX 130. The multiplexed signals are simultaneously transmitted through an optical fiber. Then, the multiplexed signals are transmitted to an opposing receiving-side WDM device in which the MUX/DEMUX 130 demultiplexes the multiplexed signals back to original signals. In this manner, the optical fiber can be used with improved efficiency.
Currently, the WDM device is not capable of multiplexing a plurality of signals of the same wavelength λ. Therefore, wavelengths λ of the signals should be set at the wavelength-converting unit 110 such that the wavelengths λ of the signals received at the MUX/DEMUX 130 do not overlap with each other.
In order to set wavelengths λ at the wavelength-converting unit 110, the operator needs to know available wavelengths λ and set different wavelengths λ for each of the channels to be multiplexed. Therefore, a wavelength-setting operation is burdensome for the operator. Also, it is expected that the numbers of channels to be multiplexed will increase in the future. For at least the reasons described above, there is a need for a method of facilitating the wavelength-setting operation for a wavelength-multiplexing process.
2. Description of the Related Art
FIG. 2 is a diagram showing an example of a WDM device of the related art. Herein, “upstream” is to be understood as a position nearer to the MUX/DEMUX 130 side and “downstream” is to be understood as a position nearer to the optical transmission devices 200-1, . . . , 200-n. In this example, upstream input terminals of the wavelength-converting unit 110 are capable of receiving a plurality of different wavelengths λ. Therefore, it is not necessary to set wavelengths λ for transmissions from downstream output terminals of the wavelength interface unit 120 to the upstream input terminal of the wavelength-converting unit 110. On the other hand, each of the downstream input terminals of the wavelength interface unit 120 is configured to receive a fixed wavelength λ for each channel. Therefore, the operator no longer needs to set wavelengths λ for transmission from the upstream output terminals of the wavelength-converting unit 110 and the downstream input terminals of the wavelength interface unit 120.
For each of channels of the wavelength-converting unit 110, a range of wavelength λ that can be configured (configurable λ-range) is predetermined. Therefore, the operator needs to configure a wavelength λ of each channel on the basis of a wavelength λ that can be used at wavelength interface subunits of the wavelength interface unit and on a predetermined range of wavelength λ that can be set in the wavelength-converting unit 110 connected to the wavelength interface unit 120 via an optical fiber. The wavelength λ is, for example, configured in a manner described below (see FIGS. 3, 4A and 4B).
The operator operates a control part 121 of the wavelength interface unit 120 to input a request for causing the wavelength interface unit 120 to change into an operating state (step S1).
The operator looks up for wavelength λ that can be received by the wavelength interface subunits of the wavelength interface unit 120 that is to be set up (step S2).
The operator looks up for a range of the wavelength λ that can be configured (configurable range) to the wavelength-converting subunits of the wavelength-converting unit 110 connected to the corresponding wavelength interface subunits of the wavelength interface unit 120 (step S3).
The operator specifies wavelength λ and sends a request to the control part 111 of the wavelength-converting unit 110 for setting the specified wavelength λ (step S4).
The control part 111 searches for the specified wavelength λ in the configurable λ-range (step S5).
It is determined whether the specified wavelength λ is in the configurable λ-range and can be output as a wavelength λ of the relevant wavelength-converting subunit of the wavelength-converting unit 110 (step S6).
If it is determined that the specified wavelength λ cannot be output (step S6, NO), an NG signal is sent to inform the operator that the specified λ cannot be set. Then, steps S2 to S5 are repeated.
If it is determined that the specified wavelength λ can be output (step S6, YES), an OK signal is sent to the operator to inform that the specified λ can be set. Then, the operator sets the specified λ as a wavelength λ for the relevant wavelength-converting subunit of the wavelength-converting unit 110 and sends main signals to the wavelength interface unit 120 using the specified λ (step S7).
The operator confirms whether optical transmission, or the main signal, using the specified wavelength λ is received at the wavelength interface unit 120 (step S8).
If reception of the optical transmission is confirmed, the wavelength setting operation is terminated. If reception of the optical transmission is not confirmed, steps S2 to S8 are repeated.
Steps S1 to S8 are repeated for each channel.
There are several drawbacks with such a wavelength-setting operation of the related art.
First, since each of the downstream input terminals of the wavelength interface unit 120 can receive a fixed wavelength, the operator needs to search for a usable wavelength λ. If the operator mistakenly sets the wavelength λ, the data cannot be transmitted and a setting operation of the wavelength λ must be performed again.
Second, the wavelength-setting operation of the related art requires many steps of complicated manual operations by the operator. This may result in man-caused erroneous operations.
Third, according to the wavelength setting operation of the related art, wavelength setting should be repeated for a number of channels to be multiplexed. Therefore, it requires considerable efforts by the operator.
Fourth, according to the wavelength setting operation of the related art, the operator is not informed of alteration of connected channels. Therefore, the user may try to transmit signals using an erroneously specified wavelength. In such a case, data cannot be transmitted until the operator becomes aware of the error and reconfigures the wavelength.